Start with the obvious. Make sure the inside of the terminals aren't crusty looking. They can be free from acid deposits but this layer can cause poor contact. Make sure the inside of the terminals are shiny. This could explain the idling problem because the computer is losing power and the idle strategy is stored in volatile memory. Also check the 6 ga. wire going to the PDC for similar problems. Check and make sure all the grounds are clean and tight from the battery.